Deep-learning magnetic resonance imaging-based automatic segmentation for organs-at-risk in the brain: Accuracy and impact on dose distribution.

Background and purpose: Normal tissue sparing in radiotherapy relies on proper delineation. While manual contouring is time consuming and subject to inter-observer variability, auto-contouring could optimize workflows and harmonize practice. We assessed the accuracy of a commercial, deep-learning, MRI-based tool for brain organs-at-risk delineation. Materials and methods: Thirty adult brain tumor patients were retrospectively manually recontoured. Two additional structure sets were obtained: AI (artificial intelligence) and AIedit (manually corrected auto-contours). For 15 selected cases, identical plans were optimized for each structure set. We used Dice Similarity Coefficient (DSC) and mean surface-distance (MSD) for geometric comparison and gamma analysis and dose-volume-histogram comparison for dose metrics evaluation. Wilcoxon signed-ranks test was used for paired data, Spearman coefficient(ρ) for correlations and Bland-Altman plots to assess level of agreement. Results: Auto-contouring was significantly faster than manual (1.1/20 min, p < 0.01). Median DSC and MSD were 0.7/0.9 mm for AI and 0.8/0.5 mm for AIedit. DSC was significantly correlated with structure size (ρ = 0.76, p < 0.01), with higher DSC for large structures. Median gamma pass rate was 74% (71-81%) for Plan_AI and 82% (75-86%) for Plan_AIedit, with no correlation with DSC or MSD. Differences between Dmean_AI and Dmean_Ref were ≤ 0.2 Gy (p < 0.05). The dose difference was moderately correlated with DSC. Bland Altman plot showed minimal discrepancy (0.1/0) between AI and reference Dmean/Dmax. Conclusions: The AI-model showed good accuracy for large structures, but developments are required for smaller ones. Auto-segmentation was significantly faster, with minor differences in dose distribution caused by geometric variations.

Improving Néel Domain Walls Dynamics and Skyrmion Stability Using He Ion Irradiation.

Ion irradiation with light ions is an appealing way to finely tune the magnetic properties of thin magnetic films and in particular the perpendicular magnetic anisotropy (PMA). In this work, the effect of He+ irradiation on the magnetization reversal and on the domain wall dynamics  of Pt/Co/AlOx trilayers is illustrated. Fluences up to 1.5 × 1015 ions cm-2 strongly decrease the PMA, without affecting neither the spontaneous magnetization nor the strength of the interfacial Dzyaloshinskii-Moriya interaction (DMI). This confirms experimentally the robustness of the DMI interaction against interfacial chemical intermixing, already predicted by theory. In parallel with the decrease of the PMA, a strong decrease of the domain wall depinning field is observed after irradiation. This allows the domain walls to reach large maximum velocities with a lower magnetic field compared to that needed for the pristine films. Decoupling PMA from DMI can, therefore, be beneficial for the design of low energy devices based on domain wall dynamics. When the samples are irradiated with larger He+ fluences, the magnetization gets close to the out-of-plane/in-plane reorientation transition, where ≈100nm size magnetic skyrmions are stabilized. It is observed that as the He+ fluence increases, the skyrmion size decreases while these magnetic textures become more stable against the application of an external magnetic field, as predicted by theoretical models developed for ultrathin films with labyrinthine domains.

Kinetics of Ion Migration in the Electric Field-Driven Manipulation of Magnetic Anisotropy of Pt/Co/Oxide Multilayers.

Magneto-ionics is a fast developing research field which opens the perspective of energy efficient magnetic devices, where the magnetization direction is controlled by an electric field which drives the migration of ionic species. In this work, the interfacial perpendicular magnetic anisotropy (PMA) of Pt/Co/oxide stacks covered by ZrO2 , acting as a ionic conductor, is tuned by a gate voltage at room temperature. A large variation of the PMA is obtained by modifying the oxidation of the cobalt layer through the migration of oxygen ions: the easy magnetization axis can be switched reversibly from in-plane, with under-oxidized Co, to in-plane, with over-oxidized Co, passing through an out-of-plane magnetization state. The switching time between the different magnetic states is limited by the ion drift velocity. This depends exponentially on the gate voltage, and is varied by over five orders of magnitude, from several minutes to a few ms. The variation of the PMA versus time during the application of the gate voltage can be modeled with a parabolic variation of the PMA and an exponential decrease of the Co oxidation rate. The possibility to explain the observed effect with a simple theoretical model opens the possibility to engineer materials with optimized properties.

IR, Raman and SERS analysis of amikacin combined with DFT-based calculations.

Amikacin, a molecule formed by two glucosamine rings linked by α-linkages through a central deoxystreptamine, is an antibiotic often used in clinical treatments, with a special attention in the pediatric cases, due to the physiological activity of their renal system. In spite of its extensive use, no detailed information about the vibrational features of the molecule is available in the literature. Thus, in this study we performed a comprehensive vibrational investigation of amikacin from both an experimental and theoretical point of view. Raman and IR spectroscopy combined with DFT calculations conducted to a complete vibrational characterization of the molecule, with the assignment of the vibrational modes. Moreover, SERS spectrum was recorded and analyzed and provided information about the adsorption behavior of the amikacin on the silver nanoparticles surface.